Viewing Saturn’s rings soon? Read me 1st

James Martin in Albuquerque, New Mexico, caught this wonderful photo of Saturn at last year’s opposition on June 15, 2017. Opposition marks the middle of the best time of year to see a planet. The 2018 opposition will happen on June 27.

It’s that magical time of year again, when the solar system’s favorite planet – Saturn – is well placed for viewing in our sky. Shining with a distinct golden color, Saturn is a lovely object to view with the eye alone. Binoculars will enhance its color … but to see Saturn’s rings you need a small telescope. And we do mean small. Veteran observer Alan MacRobert at SkyandTelescope.com has written:

The rings of Saturn should be visible in even the smallest telescope at 25x [magnified by 25 times]. A good 3-inch ‘scope at 50x [magnified by 50 times] can show them as a separate structure detached on all sides from the ball of the planet.

Help EarthSky keep going! Please donate what you can to our annual crowd-funding campaign.

You want to see Saturn’s rings. We know you do! Here are some basics:

1. Telescope. Don’t expect to see the rings in binoculars. You really do need a telescope. Don’t have one? Maybe there’s an astronomy club near you that will hold a star party in the near future. The links below might help you find one.

Astronomy Clubs Near Me & Organizations

2018 Astronomy Club Directory

NASA’s Night Sky Network

Astronomy Clubs Near Me

These images suggest how the ringed planet Saturn might look when seen through a telescope with an aperture 4 inches (100 mm) in diameter (top) and through a larger instrument with an 8-inch aperture (bottom). Image via SkyandTelescope.com/NASA/Hubble Space Telescope.

2. Tilt. The big night has come. You’re going to look through a telescope and see Saturn’s rings! Note the tilt of the rings. As with so much in space (and on Earth), the appearance of Saturn’s rings from Earth is cyclical. In 2017, the north side of the rings opened up most widely (27 degrees), as seen from Earth. That’s the most open this face of the rings has been since since 1988. In 2018, we’re past the peak of the north ring face opening, but Saturn’s rings are still inclined at about 26 degrees from edge-on, still exhibiting their northern face. By the year 2025, by the way, the rings will appear edge-on as seen from Earth. After that, we’ll begin to see the south side of Saturn’s rings and their openness will gradually increase to a maximum inclination of 27 degrees by May 2032.

The tilt of Saturn’s rings has a great impact on the planet’s overall brightness as seen from Earth. That’s why – although 2018’s opposition is distant – the planet isn’t particularly dim this year. In years when Saturn’s rings are edge-on as seen from Earth (2009 and 2025), Saturn does appear considerably dimmer than in years when Saturn’s rings are maximally tilted toward Earth (2017 and 2032). Image via Wikimedia Commons.

3. 3-D. Ask yourself … do Saturn’s rings look 3-dimensional? Again quoting Alan MacRobert at SkyandTelescope.com:

Saturn has a more three-dimensional appearance than any other object in the sky — at least that’s how it looks to me with a 6-inch scope on a night of fine seeing.

4. Seeing. What was Alan talking about in that quote above when he mentioned seeing? Both amateur and professional astronomers talk about the night’s seeing, which affects how clearly and sharply you can see a telescopic image. Seeing isn’t a quality of the telescope; it’s a quality of the air above you. It’s the reason the stars twinkle more on some nights than others. When the air is particularly turbulent, astronomers say there’s bad seeing. The images at the telescope shimmy and dance. When the air is particularly still, astronomers say there’s good seeing. Seeing can shift from moment to moment, as parcels of air move above you. So, as you’re gazing at Saturn, stand as quietly as you can – for as long as you can – and just look. You’ll notice moments when the image suddenly comes into sharper focus.

Turbulent air makes for poor seeing. But the air above you can also “settle” suddenly. When viewing Saturn, wait for those moments. Image via AstronomyNotes.com.

5. Other things to think about. Once you get comfortable viewing Saturn – assuming you’re able to view it again and again, with a telescope of your own – you’ll begin to notice details in the rings. Today, thanks to spacecraft, we know that Saturn’s rings are incredibly detailed. But, as you stand at your telescope gazing upward, you might be thrilled to witness just one primary division in the rings, the Cassini Division between the A and B rings, named for its French discoverer Jean D. Cassini. Seeing this dark division is a good test of the night’s seeing and your telescope’s optical quality, and also of your own eyes’ ability to simply look and notice what you see. By the way, if you’re looking at the rings – which means you’re viewing Saturn through a telescope – look also for one or more of Saturn’s many moons, most notably Titan.

Have fun!

Alas, you won’t see Saturn look like this through a telescope. This is a spacecraft view, from Cassini in 2016, showing Saturn’s northern hemisphere. Image via NASA/JPL-Caltech/Space Science Institute.

Bottom line: In 2018, Saturn’s opposition – marking the middle of the best time of year to see it – comes on June 27. Here are some tips for beginners, either those with new telescopes or those attending star parties, for things to look for and think about when you are planning to see Saturn’s rings.

Read more … Viewing Saturn: Rings, Planet and Moons

Help EarthSky keep going! Please donate what you can to our annual crowd-funding campaign.

from EarthSky https://ift.tt/2J50r7B

James Martin in Albuquerque, New Mexico, caught this wonderful photo of Saturn at last year’s opposition on June 15, 2017. Opposition marks the middle of the best time of year to see a planet. The 2018 opposition will happen on June 27.

It’s that magical time of year again, when the solar system’s favorite planet – Saturn – is well placed for viewing in our sky. Shining with a distinct golden color, Saturn is a lovely object to view with the eye alone. Binoculars will enhance its color … but to see Saturn’s rings you need a small telescope. And we do mean small. Veteran observer Alan MacRobert at SkyandTelescope.com has written:

The rings of Saturn should be visible in even the smallest telescope at 25x [magnified by 25 times]. A good 3-inch ‘scope at 50x [magnified by 50 times] can show them as a separate structure detached on all sides from the ball of the planet.

Help EarthSky keep going! Please donate what you can to our annual crowd-funding campaign.

You want to see Saturn’s rings. We know you do! Here are some basics:

1. Telescope. Don’t expect to see the rings in binoculars. You really do need a telescope. Don’t have one? Maybe there’s an astronomy club near you that will hold a star party in the near future. The links below might help you find one.

Astronomy Clubs Near Me & Organizations

2018 Astronomy Club Directory

NASA’s Night Sky Network

Astronomy Clubs Near Me

These images suggest how the ringed planet Saturn might look when seen through a telescope with an aperture 4 inches (100 mm) in diameter (top) and through a larger instrument with an 8-inch aperture (bottom). Image via SkyandTelescope.com/NASA/Hubble Space Telescope.

2. Tilt. The big night has come. You’re going to look through a telescope and see Saturn’s rings! Note the tilt of the rings. As with so much in space (and on Earth), the appearance of Saturn’s rings from Earth is cyclical. In 2017, the north side of the rings opened up most widely (27 degrees), as seen from Earth. That’s the most open this face of the rings has been since since 1988. In 2018, we’re past the peak of the north ring face opening, but Saturn’s rings are still inclined at about 26 degrees from edge-on, still exhibiting their northern face. By the year 2025, by the way, the rings will appear edge-on as seen from Earth. After that, we’ll begin to see the south side of Saturn’s rings and their openness will gradually increase to a maximum inclination of 27 degrees by May 2032.

The tilt of Saturn’s rings has a great impact on the planet’s overall brightness as seen from Earth. That’s why – although 2018’s opposition is distant – the planet isn’t particularly dim this year. In years when Saturn’s rings are edge-on as seen from Earth (2009 and 2025), Saturn does appear considerably dimmer than in years when Saturn’s rings are maximally tilted toward Earth (2017 and 2032). Image via Wikimedia Commons.

3. 3-D. Ask yourself … do Saturn’s rings look 3-dimensional? Again quoting Alan MacRobert at SkyandTelescope.com:

Saturn has a more three-dimensional appearance than any other object in the sky — at least that’s how it looks to me with a 6-inch scope on a night of fine seeing.

4. Seeing. What was Alan talking about in that quote above when he mentioned seeing? Both amateur and professional astronomers talk about the night’s seeing, which affects how clearly and sharply you can see a telescopic image. Seeing isn’t a quality of the telescope; it’s a quality of the air above you. It’s the reason the stars twinkle more on some nights than others. When the air is particularly turbulent, astronomers say there’s bad seeing. The images at the telescope shimmy and dance. When the air is particularly still, astronomers say there’s good seeing. Seeing can shift from moment to moment, as parcels of air move above you. So, as you’re gazing at Saturn, stand as quietly as you can – for as long as you can – and just look. You’ll notice moments when the image suddenly comes into sharper focus.

Turbulent air makes for poor seeing. But the air above you can also “settle” suddenly. When viewing Saturn, wait for those moments. Image via AstronomyNotes.com.

5. Other things to think about. Once you get comfortable viewing Saturn – assuming you’re able to view it again and again, with a telescope of your own – you’ll begin to notice details in the rings. Today, thanks to spacecraft, we know that Saturn’s rings are incredibly detailed. But, as you stand at your telescope gazing upward, you might be thrilled to witness just one primary division in the rings, the Cassini Division between the A and B rings, named for its French discoverer Jean D. Cassini. Seeing this dark division is a good test of the night’s seeing and your telescope’s optical quality, and also of your own eyes’ ability to simply look and notice what you see. By the way, if you’re looking at the rings – which means you’re viewing Saturn through a telescope – look also for one or more of Saturn’s many moons, most notably Titan.

Have fun!

Alas, you won’t see Saturn look like this through a telescope. This is a spacecraft view, from Cassini in 2016, showing Saturn’s northern hemisphere. Image via NASA/JPL-Caltech/Space Science Institute.

Bottom line: In 2018, Saturn’s opposition – marking the middle of the best time of year to see it – comes on June 27. Here are some tips for beginners, either those with new telescopes or those attending star parties, for things to look for and think about when you are planning to see Saturn’s rings.

Read more … Viewing Saturn: Rings, Planet and Moons

Help EarthSky keep going! Please donate what you can to our annual crowd-funding campaign.

from EarthSky https://ift.tt/2J50r7B

The Standard Model theory of particle physics

How does our world work on a subatomic level? Image via Varsha Y S.

By Glenn Starkman, Case Western Reserve University

The Standard Model. What dull name for the most accurate scientific theory known to human beings.

More than a quarter of the Nobel Prizes in physics of the last century are direct inputs to or direct results of the Standard Model. Yet its name suggests that if you can afford a few extra dollars a month you should buy the upgrade. As a theoretical physicist, I’d prefer The Absolutely Amazing Theory of Almost Everything. That’s what the Standard Model really is.

Many recall the excitement among scientists and media over the 2012 discovery of the Higgs boson. But that much-ballyhooed event didn’t come out of the blue – it capped a five-decade undefeated streak for the Standard Model. Every fundamental force but gravity is included in it. Every attempt to overturn it to demonstrate in the laboratory that it must be substantially reworked – and there have been many over the past 50 years – has failed.

In short, the Standard Model answers this question: What is everything made of, and how does it hold together?

The smallest building blocks

You know, of course, that the world around us is made of molecules, and molecules are made of atoms. Chemist Dmitri Mendeleev figured that out in the 1860s and organized all atoms – that is, the elements – into the periodic table that you probably studied in middle school. But there are 118 different chemical elements. There’s antimony, arsenic, aluminum, selenium … and 114 more.

Our annual crowd-funding campaign has started. Please donate what you can to help EarthSky keep going!

But these elements can be broken down further. Image via Rubén Vera Koster.

Physicists like things simple. We want to boil things down to their essence, a few basic building blocks. Over a hundred chemical elements is not simple. The ancients believed that everything is made of just five elements – earth, water, fire, air and aether. Five is much simpler than 118. It’s also wrong.

By 1932, scientists knew that all those atoms are made of just three particles – neutrons, protons and electrons. The neutrons and protons are bound together tightly into the nucleus. The electrons, thousands of times lighter, whirl around the nucleus at speeds approaching that of light. Physicists Planck, Bohr, Schroedinger, Heisenberg and friends had invented a new science – quantum mechanics – to explain this motion.

That would have been a satisfying place to stop. Just three particles. Three is even simpler than five. But held together how? The negatively charged electrons and positively charged protons are bound together by electromagnetism. But the protons are all huddled together in the nucleus and their positive charges should be pushing them powerfully apart. The neutral neutrons can’t help.

What binds these protons and neutrons together? “Divine intervention” a man on a Toronto street corner told me; he had a pamphlet, I could read all about it. But this scenario seemed like a lot of trouble even for a divine being – keeping tabs on every single one of the universe’s 10?? protons and neutrons and bending them to its will.

Expanding the zoo of particles

Meanwhile, nature cruelly declined to keep its zoo of particles to just three. Really four, because we should count the photon, the particle of light that Einstein described. Four grew to five when Anderson measured electrons with positive charge – positrons – striking the Earth from outer space. At least Dirac had predicted these first anti-matter particles. Five became six when the pion, which Yukawa predicted would hold the nucleus together, was found.

Then came the muon – 200 times heavier than the electron, but otherwise a twin. “Who ordered that?” I.I. Rabi quipped. That sums it up. Number seven. Not only not simple, redundant.

By the 1960s there were hundreds of “fundamental” particles. In place of the well-organized periodic table, there were just long lists of baryons (heavy particles like protons and neutrons), mesons (like Yukawa’s pions) and leptons (light particles like the electron, and the elusive neutrinos) – with no organization and no guiding principles.

Into this breach sidled the Standard Model. It was not an overnight flash of brilliance. No Archimedes leapt out of a bathtub shouting “eureka.” Instead, there was a series of crucial insights by a few key individuals in the mid-1960s that transformed this quagmire into a simple theory, and then five decades of experimental verification and theoretical elaboration.

Quarks. They come in six varieties we call flavors. Like ice cream, except not as tasty. Instead of vanilla, chocolate and so on, we have up, down, strange, charm, bottom and top. In 1964, Gell-Mann and Zweig taught us the recipes: Mix and match any three quarks to get a baryon. Protons are two ups and a down quark bound together; neutrons are two downs and an up. Choose one quark and one antiquark to get a meson. A pion is an up or a down quark bound to an anti-up or an anti-down. All the material of our daily lives is made of just up and down quarks and anti-quarks and electrons.

The Standard Model of elementary particles provides an ingredients list for everything around us. Image via Fermi National Accelerator Laboratory.

Simple. Well, simple-ish, because keeping those quarks bound is a feat. They are tied to one another so tightly that you never ever find a quark or anti-quark on its own. The theory of that binding, and the particles called gluons (chuckle) that are responsible, is called quantum chromodynamics. It’s a vital piece of the Standard Model, but mathematically difficult, even posing an unsolved problem of basic mathematics. We physicists do our best to calculate with it, but we’re still learning how.

The other aspect of the Standard Model is “A Model of Leptons.” That’s the name of the landmark 1967 paper by Steven Weinberg that pulled together quantum mechanics with the vital pieces of knowledge of how particles interact and organized the two into a single theory. It incorporated the familiar electromagnetism, joined it with what physicists called “the weak force” that causes certain radioactive decays, and explained that they were different aspects of the same force. It incorporated the Higgs mechanism for giving mass to fundamental particles.

Since then, the Standard Model has predicted the results of experiment after experiment, including the discovery of several varieties of quarks and of the W and Z bosons – heavy particles that are for weak interactions what the photon is for electromagnetism. The possibility that neutrinos aren’t massless was overlooked in the 1960s, but slipped easily into the Standard Model in the 1990s, a few decades late to the party.

3D view of an event recorded at the CERN particle accelerator showing characteristics expected from the decay of the SM Higgs boson to a pair of photons (dashed yellow lines and green towers). Image via McCauley, Thomas; Taylor, Lucas; for the CMS Collaboration CERN.

Discovering the Higgs boson in 2012, long predicted by the Standard Model and long sought after, was a thrill but not a surprise. It was yet another crucial victory for the Standard Model over the dark forces that particle physicists have repeatedly warned loomed over the horizon. Concerned that the Standard Model didn’t adequately embody their expectations of simplicity, worried about its mathematical self-consistency, or looking ahead to the eventual necessity to bring the force of gravity into the fold, physicists have made numerous proposals for theories beyond the Standard Model. These bear exciting names like Grand Unified Theories, Supersymmetry, Technicolor, and String Theory.

Sadly, at least for their proponents, beyond-the-Standard-Model theories have not yet successfully predicted any new experimental phenomenon or any experimental discrepancy with the Standard Model.

After five decades, far from requiring an upgrade, the Standard Model is worthy of celebration as the Absolutely Amazing Theory of Almost Everything.

Glenn Starkman, Distinguished University Professor of Physics, Case Western Reserve University

This article was originally published on The Conversation. Read the original article.

Bottom line: What is The Standard Model theory of particle physics?

from EarthSky https://ift.tt/2kCdiDv

How does our world work on a subatomic level? Image via Varsha Y S.

By Glenn Starkman, Case Western Reserve University

The Standard Model. What dull name for the most accurate scientific theory known to human beings.

More than a quarter of the Nobel Prizes in physics of the last century are direct inputs to or direct results of the Standard Model. Yet its name suggests that if you can afford a few extra dollars a month you should buy the upgrade. As a theoretical physicist, I’d prefer The Absolutely Amazing Theory of Almost Everything. That’s what the Standard Model really is.

Many recall the excitement among scientists and media over the 2012 discovery of the Higgs boson. But that much-ballyhooed event didn’t come out of the blue – it capped a five-decade undefeated streak for the Standard Model. Every fundamental force but gravity is included in it. Every attempt to overturn it to demonstrate in the laboratory that it must be substantially reworked – and there have been many over the past 50 years – has failed.

In short, the Standard Model answers this question: What is everything made of, and how does it hold together?

The smallest building blocks

You know, of course, that the world around us is made of molecules, and molecules are made of atoms. Chemist Dmitri Mendeleev figured that out in the 1860s and organized all atoms – that is, the elements – into the periodic table that you probably studied in middle school. But there are 118 different chemical elements. There’s antimony, arsenic, aluminum, selenium … and 114 more.

Our annual crowd-funding campaign has started. Please donate what you can to help EarthSky keep going!

But these elements can be broken down further. Image via Rubén Vera Koster.

Physicists like things simple. We want to boil things down to their essence, a few basic building blocks. Over a hundred chemical elements is not simple. The ancients believed that everything is made of just five elements – earth, water, fire, air and aether. Five is much simpler than 118. It’s also wrong.

By 1932, scientists knew that all those atoms are made of just three particles – neutrons, protons and electrons. The neutrons and protons are bound together tightly into the nucleus. The electrons, thousands of times lighter, whirl around the nucleus at speeds approaching that of light. Physicists Planck, Bohr, Schroedinger, Heisenberg and friends had invented a new science – quantum mechanics – to explain this motion.

That would have been a satisfying place to stop. Just three particles. Three is even simpler than five. But held together how? The negatively charged electrons and positively charged protons are bound together by electromagnetism. But the protons are all huddled together in the nucleus and their positive charges should be pushing them powerfully apart. The neutral neutrons can’t help.

What binds these protons and neutrons together? “Divine intervention” a man on a Toronto street corner told me; he had a pamphlet, I could read all about it. But this scenario seemed like a lot of trouble even for a divine being – keeping tabs on every single one of the universe’s 10?? protons and neutrons and bending them to its will.

Expanding the zoo of particles

Meanwhile, nature cruelly declined to keep its zoo of particles to just three. Really four, because we should count the photon, the particle of light that Einstein described. Four grew to five when Anderson measured electrons with positive charge – positrons – striking the Earth from outer space. At least Dirac had predicted these first anti-matter particles. Five became six when the pion, which Yukawa predicted would hold the nucleus together, was found.

Then came the muon – 200 times heavier than the electron, but otherwise a twin. “Who ordered that?” I.I. Rabi quipped. That sums it up. Number seven. Not only not simple, redundant.

By the 1960s there were hundreds of “fundamental” particles. In place of the well-organized periodic table, there were just long lists of baryons (heavy particles like protons and neutrons), mesons (like Yukawa’s pions) and leptons (light particles like the electron, and the elusive neutrinos) – with no organization and no guiding principles.

Into this breach sidled the Standard Model. It was not an overnight flash of brilliance. No Archimedes leapt out of a bathtub shouting “eureka.” Instead, there was a series of crucial insights by a few key individuals in the mid-1960s that transformed this quagmire into a simple theory, and then five decades of experimental verification and theoretical elaboration.

Quarks. They come in six varieties we call flavors. Like ice cream, except not as tasty. Instead of vanilla, chocolate and so on, we have up, down, strange, charm, bottom and top. In 1964, Gell-Mann and Zweig taught us the recipes: Mix and match any three quarks to get a baryon. Protons are two ups and a down quark bound together; neutrons are two downs and an up. Choose one quark and one antiquark to get a meson. A pion is an up or a down quark bound to an anti-up or an anti-down. All the material of our daily lives is made of just up and down quarks and anti-quarks and electrons.

The Standard Model of elementary particles provides an ingredients list for everything around us. Image via Fermi National Accelerator Laboratory.

Simple. Well, simple-ish, because keeping those quarks bound is a feat. They are tied to one another so tightly that you never ever find a quark or anti-quark on its own. The theory of that binding, and the particles called gluons (chuckle) that are responsible, is called quantum chromodynamics. It’s a vital piece of the Standard Model, but mathematically difficult, even posing an unsolved problem of basic mathematics. We physicists do our best to calculate with it, but we’re still learning how.

The other aspect of the Standard Model is “A Model of Leptons.” That’s the name of the landmark 1967 paper by Steven Weinberg that pulled together quantum mechanics with the vital pieces of knowledge of how particles interact and organized the two into a single theory. It incorporated the familiar electromagnetism, joined it with what physicists called “the weak force” that causes certain radioactive decays, and explained that they were different aspects of the same force. It incorporated the Higgs mechanism for giving mass to fundamental particles.

Since then, the Standard Model has predicted the results of experiment after experiment, including the discovery of several varieties of quarks and of the W and Z bosons – heavy particles that are for weak interactions what the photon is for electromagnetism. The possibility that neutrinos aren’t massless was overlooked in the 1960s, but slipped easily into the Standard Model in the 1990s, a few decades late to the party.

3D view of an event recorded at the CERN particle accelerator showing characteristics expected from the decay of the SM Higgs boson to a pair of photons (dashed yellow lines and green towers). Image via McCauley, Thomas; Taylor, Lucas; for the CMS Collaboration CERN.

Discovering the Higgs boson in 2012, long predicted by the Standard Model and long sought after, was a thrill but not a surprise. It was yet another crucial victory for the Standard Model over the dark forces that particle physicists have repeatedly warned loomed over the horizon. Concerned that the Standard Model didn’t adequately embody their expectations of simplicity, worried about its mathematical self-consistency, or looking ahead to the eventual necessity to bring the force of gravity into the fold, physicists have made numerous proposals for theories beyond the Standard Model. These bear exciting names like Grand Unified Theories, Supersymmetry, Technicolor, and String Theory.

Sadly, at least for their proponents, beyond-the-Standard-Model theories have not yet successfully predicted any new experimental phenomenon or any experimental discrepancy with the Standard Model.

After five decades, far from requiring an upgrade, the Standard Model is worthy of celebration as the Absolutely Amazing Theory of Almost Everything.

Glenn Starkman, Distinguished University Professor of Physics, Case Western Reserve University

This article was originally published on The Conversation. Read the original article.

Bottom line: What is The Standard Model theory of particle physics?

from EarthSky https://ift.tt/2kCdiDv

Today is Walt Whitman’s birthday

Walt Whitman by Thomas Eakins, 1887-88

May 31, 1819. Today is the birthday of Walt Whitman, poet and journalist, born in West Hills, New York. He’s considered one of America’s most influential poets, and his collection Leaves of Grass is considered a landmark in American literature. Would Whitman himself approved of celebrating his birthday on a science website like EarthSky? After all, he was a poet. But this quote by itself caused us to include him:

This is what you shall do; Love the earth and sun and the animals, despise riches, give alms to every one that asks, stand up for the stupid and crazy, devote your income and labor to others, hate tyrants, argue not concerning God, have patience and indulgence toward the people, take off your hat to nothing known or unknown or to any man or number of men, go freely with powerful uneducated persons and with the young and with the mothers of families, read these leaves in the open air every season of every year of your life, re-examine all you have been told at school or church or in any book, dismiss whatever insults your own soul, and your very flesh shall be a great poem and have the richest fluency not only in its words but in the silent lines of its lips and face and between the lashes of your eyes and in every motion and joint of your body.

Do these ideas remind you of science? Not yet? Then how about this one?

I believe a leaf of grass is no less than the journey-work of the stars.

Enjoying EarthSky so far? Sign up for our free daily newsletter today!

Walt Whitman as photographed by Matthew Brady.

Bottom line: Walt Whitman was born on May 31, 1819.

from EarthSky https://ift.tt/1KFOdQk

Walt Whitman by Thomas Eakins, 1887-88

May 31, 1819. Today is the birthday of Walt Whitman, poet and journalist, born in West Hills, New York. He’s considered one of America’s most influential poets, and his collection Leaves of Grass is considered a landmark in American literature. Would Whitman himself approved of celebrating his birthday on a science website like EarthSky? After all, he was a poet. But this quote by itself caused us to include him:

This is what you shall do; Love the earth and sun and the animals, despise riches, give alms to every one that asks, stand up for the stupid and crazy, devote your income and labor to others, hate tyrants, argue not concerning God, have patience and indulgence toward the people, take off your hat to nothing known or unknown or to any man or number of men, go freely with powerful uneducated persons and with the young and with the mothers of families, read these leaves in the open air every season of every year of your life, re-examine all you have been told at school or church or in any book, dismiss whatever insults your own soul, and your very flesh shall be a great poem and have the richest fluency not only in its words but in the silent lines of its lips and face and between the lashes of your eyes and in every motion and joint of your body.

Do these ideas remind you of science? Not yet? Then how about this one?

I believe a leaf of grass is no less than the journey-work of the stars.

Enjoying EarthSky so far? Sign up for our free daily newsletter today!

Walt Whitman as photographed by Matthew Brady.

Bottom line: Walt Whitman was born on May 31, 1819.

from EarthSky https://ift.tt/1KFOdQk

Planet-hunter Kepler keeps going as fuel dwindles

Illustration depicting objects Kepler will explore during its 18th observing campaign. Image via NASA Ames Research Center/ Ann Marie Cody.

The Kepler Space Telescope has revolutionized our understanding of exoplanets, or worlds orbiting other stars. It’s been the most successful planet-hunter by far, so far discovering thousands of exoplanets since 2009, with the promise of more to come. On May 23, 2018, NASA announced that Kepler has now begun the 18th observing campaign of its extended K2 mission. The campaign began on May 12, and will continue for 82 days; during that time, Kepler will focus on a variety of cosmic objects, including nearby star clusters, an infamous near-Earth asteroid called 99942 Apophis, and an exotic blazer in the distant universe called OJ 287.

This campaign covers some old ground as it were, since it focuses on almost exactly the same patch of sky as Kepler’s Campaign 5 in 2015. NASA explained:

One of the advantages of observing a field over again is that [exoplanets] may be found orbiting farther from their stars. Astronomers hope to not only discover new exoplanets during this campaign, but also to confirm candidates that were previously identified.

Indeed, to date, most exoplanets discovered by Kepler do orbit close to their stars, as they have been the easiest for the spacecraft’s observing system to detect.

Help EarthSky keep going! Our annual crowd-funding campaign begins today. Please donate what you can.

Artist’s of the Kepler Space Telescope. Unlike the Hubble, which orbits Earth, Kepler is in what’s called an Earth trailing orbit around the sun. It takes 371 days to complete one circuit, remaining always about 94 million miles (150 million km) from Earth. Image via NASA.

One of the objects Kepler is observing in this campaign is familiar to stargazers. It is Messier 44, aka Praesepe or the Beehive, located in the direction to the constellation Cancer the Crab. This is an open star cluster, like the one in which our sun is thought to have been born. Six exoplanets have already been discovered orbiting stars in the Beehive.

Kepler will also be observing Messier 67, sometimes called the King Cobra cluster, another open star cluster in Cancer.

Open clusters including Messier 67 and Messier 44 are regions where stars formed at roughly the same time. Thus, as we gaze toward these stars, we see them as approximately the same age. Kepler will be looking for exoplanets that are transiting, or crossing, in front of these stars as seen from Earth.

View larger. | EarthSky community member Tom Wildoner caught this image of the Beehive star cluster (M44) and the King Cobra cluster (M67) in 2016. This is one area will Kepler will be looking toward, in its 18th K2 mission. Read more about this image at Tom’s blog, LeisurelyScientist.com.

Kepler will have an opportunity during its 18th K2 campaign to peer toward the infamous asteroid 99942 Apophis. This near-Earth asteroid – about 1,000-foot or 300 meters in diameter – caused a stir back in 2004, when early observations of its orbit suggested a small probability (up to 2.7%) that it would hit Earth on April 13, 2029.

Further observations showed Apophis would pass within 20,000 miles (32,000 km) of Earth in the year 2029, but not strike us. As NASA said:

… close but still comfortably far enough to not pose any danger to Earthlings.

Although the probability that Apophis will strike us in 2029 is now calculated at zero, astronomers are still looking at future passes, and this near-Earth asteroid remains one of the most interesting objects out there.

Apophis is one of thousands of near-Earth asteroids routinely tracked by astronomers on Earth. Sometimes, orbiting observatories like Kepler do take a look at Apophis as well. Thus, bit by bit, we increase our understanding of Apophis. This image is from 2013, when the Herschel Space Observatory looked toward this object and acquired a 3-color view of the asteroid. Read more about this image.

But – as it gazes toward its small section of space – Kepler won’t be looking only at nearby objects. It will also be looking at blazars, the energetic nuclei of very distant galaxies with massive black holes in their centers. One such target is OJ 287, where two black holes are in orbit around each other. One of these black hole is 18 billion times the mass of our sun! That’s in contrast to the 4-million-solar-mass black hole at the center of our home galaxy, the Milky Way.

So this new observing campaign will be an exciting new chapter in Kepler’s K2 mission, and in the Kepler mission overall, which, unfortunately, will be coming to an end soon. The telescope is running out of fuel, with probably only several months left.

By the way, it’s in many ways amazing we’ve had a K2 or extended mission. Kepler’s primary mission ended in 2013 after a second reaction wheel broke. That wheel was used to help the spacecraft remain steady with a fixed gaze on its targets, and, without it, Kepler could not do its work. Later, NASA scientists were able to fix the problem – partially and, as always, cleverly – by using pressure from sunlight to help Kepler maintain position. This new phase is the extended K2 mission, and it was estimated that 10 observing campaigns would be possible with the remaining fuel.

That estimate turned out to be too conservative, with Kepler now entering its 18th observing campaign during K2. A fantastic achievement, but unfortunately there is nothing that can be done about the fuel problem. As Charlie Sobeck, a system engineer for the Kepler mission, explained in a NASA statement:

Our current estimates are that Kepler’s tank will run dry within several months – but we’ve been surprised by its performance before! So, while we anticipate flight operations ending soon, we are prepared to continue as long as the fuel allows. The Kepler team is planning to collect as much science data as possible in its remaining time and beam it back to Earth before the loss of the fuel-powered thrusters means that we can’t aim the spacecraft for data transfer. We even have plans to take some final calibration data with the last bit of fuel, if the opportunity presents itself.

Kepler, by the way, already has a replacement. The TESS planet-hunter was launched in April 2018.

Even though Kepler has discovered many, many exoplanets, it has only looked at one small part of the galaxy. Scientists now estimate that there are billions of planets in our galaxy alone. Image via Jon Lomberg/ NASA/ Wikipedia.

Bottom line: Kepler has already discovered thousands of exoplanets during its mission, of many different types, and now, during its 18th observing campaign, it should be able to find even more, as well as provide unique views of many other cosmic objects and phenomena. Even as the mission is now nearing its end, the hobbled spacecraft continues to collect as much science data as it possibly can – a fitting finale for a spacecraft which has opened wide our views of these other worlds.

Via NASA

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Illustration depicting objects Kepler will explore during its 18th observing campaign. Image via NASA Ames Research Center/ Ann Marie Cody.

The Kepler Space Telescope has revolutionized our understanding of exoplanets, or worlds orbiting other stars. It’s been the most successful planet-hunter by far, so far discovering thousands of exoplanets since 2009, with the promise of more to come. On May 23, 2018, NASA announced that Kepler has now begun the 18th observing campaign of its extended K2 mission. The campaign began on May 12, and will continue for 82 days; during that time, Kepler will focus on a variety of cosmic objects, including nearby star clusters, an infamous near-Earth asteroid called 99942 Apophis, and an exotic blazer in the distant universe called OJ 287.

This campaign covers some old ground as it were, since it focuses on almost exactly the same patch of sky as Kepler’s Campaign 5 in 2015. NASA explained:

One of the advantages of observing a field over again is that [exoplanets] may be found orbiting farther from their stars. Astronomers hope to not only discover new exoplanets during this campaign, but also to confirm candidates that were previously identified.

Indeed, to date, most exoplanets discovered by Kepler do orbit close to their stars, as they have been the easiest for the spacecraft’s observing system to detect.

Help EarthSky keep going! Our annual crowd-funding campaign begins today. Please donate what you can.

Artist’s of the Kepler Space Telescope. Unlike the Hubble, which orbits Earth, Kepler is in what’s called an Earth trailing orbit around the sun. It takes 371 days to complete one circuit, remaining always about 94 million miles (150 million km) from Earth. Image via NASA.

One of the objects Kepler is observing in this campaign is familiar to stargazers. It is Messier 44, aka Praesepe or the Beehive, located in the direction to the constellation Cancer the Crab. This is an open star cluster, like the one in which our sun is thought to have been born. Six exoplanets have already been discovered orbiting stars in the Beehive.

Kepler will also be observing Messier 67, sometimes called the King Cobra cluster, another open star cluster in Cancer.

Open clusters including Messier 67 and Messier 44 are regions where stars formed at roughly the same time. Thus, as we gaze toward these stars, we see them as approximately the same age. Kepler will be looking for exoplanets that are transiting, or crossing, in front of these stars as seen from Earth.

View larger. | EarthSky community member Tom Wildoner caught this image of the Beehive star cluster (M44) and the King Cobra cluster (M67) in 2016. This is one area will Kepler will be looking toward, in its 18th K2 mission. Read more about this image at Tom’s blog, LeisurelyScientist.com.

Kepler will have an opportunity during its 18th K2 campaign to peer toward the infamous asteroid 99942 Apophis. This near-Earth asteroid – about 1,000-foot or 300 meters in diameter – caused a stir back in 2004, when early observations of its orbit suggested a small probability (up to 2.7%) that it would hit Earth on April 13, 2029.

Further observations showed Apophis would pass within 20,000 miles (32,000 km) of Earth in the year 2029, but not strike us. As NASA said:

… close but still comfortably far enough to not pose any danger to Earthlings.

Although the probability that Apophis will strike us in 2029 is now calculated at zero, astronomers are still looking at future passes, and this near-Earth asteroid remains one of the most interesting objects out there.

Apophis is one of thousands of near-Earth asteroids routinely tracked by astronomers on Earth. Sometimes, orbiting observatories like Kepler do take a look at Apophis as well. Thus, bit by bit, we increase our understanding of Apophis. This image is from 2013, when the Herschel Space Observatory looked toward this object and acquired a 3-color view of the asteroid. Read more about this image.

But – as it gazes toward its small section of space – Kepler won’t be looking only at nearby objects. It will also be looking at blazars, the energetic nuclei of very distant galaxies with massive black holes in their centers. One such target is OJ 287, where two black holes are in orbit around each other. One of these black hole is 18 billion times the mass of our sun! That’s in contrast to the 4-million-solar-mass black hole at the center of our home galaxy, the Milky Way.

So this new observing campaign will be an exciting new chapter in Kepler’s K2 mission, and in the Kepler mission overall, which, unfortunately, will be coming to an end soon. The telescope is running out of fuel, with probably only several months left.

By the way, it’s in many ways amazing we’ve had a K2 or extended mission. Kepler’s primary mission ended in 2013 after a second reaction wheel broke. That wheel was used to help the spacecraft remain steady with a fixed gaze on its targets, and, without it, Kepler could not do its work. Later, NASA scientists were able to fix the problem – partially and, as always, cleverly – by using pressure from sunlight to help Kepler maintain position. This new phase is the extended K2 mission, and it was estimated that 10 observing campaigns would be possible with the remaining fuel.

That estimate turned out to be too conservative, with Kepler now entering its 18th observing campaign during K2. A fantastic achievement, but unfortunately there is nothing that can be done about the fuel problem. As Charlie Sobeck, a system engineer for the Kepler mission, explained in a NASA statement:

Our current estimates are that Kepler’s tank will run dry within several months – but we’ve been surprised by its performance before! So, while we anticipate flight operations ending soon, we are prepared to continue as long as the fuel allows. The Kepler team is planning to collect as much science data as possible in its remaining time and beam it back to Earth before the loss of the fuel-powered thrusters means that we can’t aim the spacecraft for data transfer. We even have plans to take some final calibration data with the last bit of fuel, if the opportunity presents itself.

Kepler, by the way, already has a replacement. The TESS planet-hunter was launched in April 2018.

Even though Kepler has discovered many, many exoplanets, it has only looked at one small part of the galaxy. Scientists now estimate that there are billions of planets in our galaxy alone. Image via Jon Lomberg/ NASA/ Wikipedia.

Bottom line: Kepler has already discovered thousands of exoplanets during its mission, of many different types, and now, during its 18th observing campaign, it should be able to find even more, as well as provide unique views of many other cosmic objects and phenomena. Even as the mission is now nearing its end, the hobbled spacecraft continues to collect as much science data as it possibly can – a fitting finale for a spacecraft which has opened wide our views of these other worlds.

Via NASA

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Manhattanhenge comes to New York

Manhattanhenge. This is a 3-image composite to preserve the disk of the sun and also shadow details of the surroundings. Gowrishankar Lakshminarayanan was in Gantry Plaza State Park, Queens, New York looking straight through 42nd Street, with the Chrysler building to the right. Canon 5D Mark III, Canon EF 70-200 F2.8 USM L Lens
Exp: ISO 100, F8.0, 1/500s/1/1000s/1/250s. HDR composite.

Every year around May 29 and 30 – and again for a day or two around July 12 – people in New York City look forward to Manhattanhenge. EarthSky community member Gowrishankar Lakshminarayanan wrote:

Manhattanhenge is a phenomenon where the sun set aligns perfectly with the streets of Manhattan, more importantly along 42nd, 34th and 14th Streets. It happens twice every year – around the end of May and early July. May 29th and 30th are the most talked-about dates in media.

As Gowri says, note that you don’t have to look on the precise dates of May 29 and 30. In fact, he captured the image above on June 1, 2017.

The phenomenon of Manhattanhenge isn’t mysterious, of course. Similar alignments occur around the world, on various dates. Think Stonehenge. The point of sunset along the horizon varies throughout the year. At this time of year – between the March equinox and June solstice – the sunset point is shifting northward each day on the horizon, as seen from around the globe. It’s the northward-shifting path of the sun that gives us summer in the Northern Hemisphere and winter in the Southern Hemisphere.

Abhijit Juvekar in Dombivli, India created this composite image of sunsets over a period of months, to show that the sun sets progressively farther north in the months leading up to the June solstice. Thank you, Abhijit!

The June solstice will bring the sun’s northernmost point in our sky – and northernmost sunset – and afterwards the sun’s path in our sky, and the sunset point, both will start shifting southward again. As for the sun’s alignment with the city of New York, and the streets of Manhattan Island, Scientific American explained:

The phenomenon is based on a design for Manhattan outlined in The Commissioners’ Plan of 1811 for a rectilinear grid, or ‘gridiron’ of straight streets and avenues that intersect one another at right angles. This design runs from north of Houston Street in Lower Manhattan to just south of 155th Street in Upper Manhattan. Most cross streets in between were arranged in a regular right-angled grid that was tilted 29 degrees east of true north to roughly replicate the angle of the island of Manhattan.

And because of this 29-degree tilt in the grid, the magic moment of the setting sun aligning with Manhattan’s cross streets does not coincide with the June solstice but rather with specific dates in late May and early July.

Read more about Manhattanhenge from ScientificAmerican.com

Bottom line:

from EarthSky https://ift.tt/2L7ot2u

Manhattanhenge. This is a 3-image composite to preserve the disk of the sun and also shadow details of the surroundings. Gowrishankar Lakshminarayanan was in Gantry Plaza State Park, Queens, New York looking straight through 42nd Street, with the Chrysler building to the right. Canon 5D Mark III, Canon EF 70-200 F2.8 USM L Lens
Exp: ISO 100, F8.0, 1/500s/1/1000s/1/250s. HDR composite.

Every year around May 29 and 30 – and again for a day or two around July 12 – people in New York City look forward to Manhattanhenge. EarthSky community member Gowrishankar Lakshminarayanan wrote:

Manhattanhenge is a phenomenon where the sun set aligns perfectly with the streets of Manhattan, more importantly along 42nd, 34th and 14th Streets. It happens twice every year – around the end of May and early July. May 29th and 30th are the most talked-about dates in media.

As Gowri says, note that you don’t have to look on the precise dates of May 29 and 30. In fact, he captured the image above on June 1, 2017.

The phenomenon of Manhattanhenge isn’t mysterious, of course. Similar alignments occur around the world, on various dates. Think Stonehenge. The point of sunset along the horizon varies throughout the year. At this time of year – between the March equinox and June solstice – the sunset point is shifting northward each day on the horizon, as seen from around the globe. It’s the northward-shifting path of the sun that gives us summer in the Northern Hemisphere and winter in the Southern Hemisphere.

Abhijit Juvekar in Dombivli, India created this composite image of sunsets over a period of months, to show that the sun sets progressively farther north in the months leading up to the June solstice. Thank you, Abhijit!

The June solstice will bring the sun’s northernmost point in our sky – and northernmost sunset – and afterwards the sun’s path in our sky, and the sunset point, both will start shifting southward again. As for the sun’s alignment with the city of New York, and the streets of Manhattan Island, Scientific American explained:

The phenomenon is based on a design for Manhattan outlined in The Commissioners’ Plan of 1811 for a rectilinear grid, or ‘gridiron’ of straight streets and avenues that intersect one another at right angles. This design runs from north of Houston Street in Lower Manhattan to just south of 155th Street in Upper Manhattan. Most cross streets in between were arranged in a regular right-angled grid that was tilted 29 degrees east of true north to roughly replicate the angle of the island of Manhattan.

And because of this 29-degree tilt in the grid, the magic moment of the setting sun aligning with Manhattan’s cross streets does not coincide with the June solstice but rather with specific dates in late May and early July.

Read more about Manhattanhenge from ScientificAmerican.com

Bottom line:

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Sunset with lightning

Image via Russ Adams.

Help EarthSky keep going! Please donate what you can to our annual crowd-funding campaign … happening now.

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Image via Russ Adams.

Help EarthSky keep going! Please donate what you can to our annual crowd-funding campaign … happening now.

from EarthSky https://ift.tt/2H1SU7y

Moon and Saturn close May 30 and 31

From around the world on May 30 and 31, 2018, you can watch for the waning gibbous moon and planet Saturn to ascend in your eastern sky in the hours after sunset. In the Northern Hemisphere, watch for them in mid-to-late evening (say, 10 to 11 p.m. local time). In the Southern Hemisphere, they’ll be up earlier (7 to 8 p.m. local time).

The moon rises first on May 30, followed by Saturn. Then, on May 31, the moon and Saturn more closely rise in unison. Click here for recommended almanacs; an almanac can give you the exact rising times for the moon and Saturn in your sky. Remember, these rising times assume an unobstructed horizon. If you have trees, mountains or whatnot blocking the sky, you’ll have to wait until later before seeing the moon and Saturn.

Just don’t mistake Jupiter for Saturn. It’s already up in the east at sunset, much brighter than the ringed planet.

Help EarthSky keep going! Our annual crowd-funding campaign begins May 30. Please donate what you can.

Here’s a photo from April’s sweep of the moon past Jupiter, Saturn and Mars. Eliot Herman in Tucson, Arizona caught the moon in between Jupiter (the bright one to the right of the moon) and 2 other planets, Mars and Saturn (the brightest 2 to the left of the moon, very close together) on April 5, 2018.

And there’s an even brighter object in your western sky after sunset. It’s Venus, the brightest of all the planets. Jupiter will lead the moon and Saturn into the sky on each of these nights (May 30 and 31). Meanwhile, around the time Venus sets for the night, you can look in the opposite direction to view the moon and Saturn coming up below Jupiter.

In other words, in late May 2018 – as viewed from mid-latitudes in the Northern Hemisphere – Venus sets in the northwest at roughly the same time that Saturn rises in the southeast. That might not be precisely true for your location on the globe … but it’ll be close. In fact, if you have an absolutely clear horizon, you might briefly see Saturn opposite of Venus in the sky, just before Venus sets.

Saturn is rising earlier daily, while Venus is setting later daily. So – if you can’t see the two together in the sky now – by the second week or so in June 2018, there’s a good chance that you’ll see Saturn opposite Venus at nightfall.

The Cassini spacecraft acquired this beautiful natural color mosaic as it soared 39 degrees above the shaded side of Saturn’s rings on May 9, 2007. Image via NASA JPL/ Space Science Institute.

On June 27, 2018, Earth will be flying more or less between Saturn and the sun. Saturn will appear opposite the sun in our sky, at what astronomers call opposition. At opposition, Saturn will rise around sunset and set around sunrise. It’ll be visible from dusk until dawn.

Jupiter was at opposition on May 9, 2018. All the superior planets – planets orbiting the sun outside of Earth’s orbit – come closest to Earth for the year at or near opposition. It’s also at opposition that a superior planet shines at its brilliant best in Earth’s sky.

Opposition happens when Earth flies between an outer planet, like Jupiter, and the sun. This happens yearly for most of the outer planets (except Mars). Illustration via Heavens Above.

Even at opposition, Saturn never gets very close to Earth. It is, after all, the most distant major planet we can see easily with the unaided eye.

What’s more, this year presents an unusually distant opposition of Saturn. This year’s opposition finds Saturn at 9 astronomical units (AU) from Earth; that’s 9 times the Earth-sun distance. It’ll be 10 AU from the sun, in other words.

Why a particularly distant opposition in 2018? It just so happens that Saturn swung to aphelion – its most distant point from the sun in its orbit – on April 17, 2018. The last time Saturn was at aphelion was September 11, 1988, and the next time won’t be until July 15, 2047.

By contrast, when Saturn is at opposition in a year when Saturn is at perihelion – nearest point to the sun in its orbit – Saturn is one AU closer to the Earth and sun than when it’s at aphelion. At opposition in those years, Saturn lodges 8 AU from Earth and 9 AU from the sun. Saturn was last at perihelion on July 26, 2003, and will next reach perihelion on November 28, 2032.

The tilt of Saturn’s rings has a great impact on the planet’s overall brightness as seen from Earth. That’s why – although 2018’s opposition is distant, the planet isn’t particularly dim this year. In years when Saturn’s rings are edge-on as seen from Earth (2009 and 2025), Saturn does appear considerably dimmer than in years when Saturn’s rings a maximally titled toward Earth (2017 and 2032). Image via Wikimedia Commons.

Surprisingly, the year 2018 doesn’t present a particularly dim opposition of Saturn – although it’s a distant opposition. That’s because the tilt of Saturn’s rings plays a big part in Saturn’s overall brightness. In 2018, Saturn’s rings tilt almost the maximum 26^o toward Earth, reflecting sunlight our way. When Saturn’s rings are edge-on, as in the years 2009 and 2025, Saturn doesn’t reflect sunlight toward Earth so its brightness is reduced in Earth’s sky.

Bottom line: Let the moon be your guide to Saturn on May 30 and 31, 2018. This planet is now nearly at its best for 2018. Its opposition will come on June 27, 2018.

Tonight – May 31, 2018 – let the moon show you the ringed planet Saturn.

from EarthSky https://ift.tt/2L87flh

From around the world on May 30 and 31, 2018, you can watch for the waning gibbous moon and planet Saturn to ascend in your eastern sky in the hours after sunset. In the Northern Hemisphere, watch for them in mid-to-late evening (say, 10 to 11 p.m. local time). In the Southern Hemisphere, they’ll be up earlier (7 to 8 p.m. local time).

The moon rises first on May 30, followed by Saturn. Then, on May 31, the moon and Saturn more closely rise in unison. Click here for recommended almanacs; an almanac can give you the exact rising times for the moon and Saturn in your sky. Remember, these rising times assume an unobstructed horizon. If you have trees, mountains or whatnot blocking the sky, you’ll have to wait until later before seeing the moon and Saturn.

Just don’t mistake Jupiter for Saturn. It’s already up in the east at sunset, much brighter than the ringed planet.

Help EarthSky keep going! Our annual crowd-funding campaign begins May 30. Please donate what you can.

Here’s a photo from April’s sweep of the moon past Jupiter, Saturn and Mars. Eliot Herman in Tucson, Arizona caught the moon in between Jupiter (the bright one to the right of the moon) and 2 other planets, Mars and Saturn (the brightest 2 to the left of the moon, very close together) on April 5, 2018.

And there’s an even brighter object in your western sky after sunset. It’s Venus, the brightest of all the planets. Jupiter will lead the moon and Saturn into the sky on each of these nights (May 30 and 31). Meanwhile, around the time Venus sets for the night, you can look in the opposite direction to view the moon and Saturn coming up below Jupiter.

In other words, in late May 2018 – as viewed from mid-latitudes in the Northern Hemisphere – Venus sets in the northwest at roughly the same time that Saturn rises in the southeast. That might not be precisely true for your location on the globe … but it’ll be close. In fact, if you have an absolutely clear horizon, you might briefly see Saturn opposite of Venus in the sky, just before Venus sets.

Saturn is rising earlier daily, while Venus is setting later daily. So – if you can’t see the two together in the sky now – by the second week or so in June 2018, there’s a good chance that you’ll see Saturn opposite Venus at nightfall.

The Cassini spacecraft acquired this beautiful natural color mosaic as it soared 39 degrees above the shaded side of Saturn’s rings on May 9, 2007. Image via NASA JPL/ Space Science Institute.

On June 27, 2018, Earth will be flying more or less between Saturn and the sun. Saturn will appear opposite the sun in our sky, at what astronomers call opposition. At opposition, Saturn will rise around sunset and set around sunrise. It’ll be visible from dusk until dawn.

Jupiter was at opposition on May 9, 2018. All the superior planets – planets orbiting the sun outside of Earth’s orbit – come closest to Earth for the year at or near opposition. It’s also at opposition that a superior planet shines at its brilliant best in Earth’s sky.

Opposition happens when Earth flies between an outer planet, like Jupiter, and the sun. This happens yearly for most of the outer planets (except Mars). Illustration via Heavens Above.

Even at opposition, Saturn never gets very close to Earth. It is, after all, the most distant major planet we can see easily with the unaided eye.

What’s more, this year presents an unusually distant opposition of Saturn. This year’s opposition finds Saturn at 9 astronomical units (AU) from Earth; that’s 9 times the Earth-sun distance. It’ll be 10 AU from the sun, in other words.

Why a particularly distant opposition in 2018? It just so happens that Saturn swung to aphelion – its most distant point from the sun in its orbit – on April 17, 2018. The last time Saturn was at aphelion was September 11, 1988, and the next time won’t be until July 15, 2047.

By contrast, when Saturn is at opposition in a year when Saturn is at perihelion – nearest point to the sun in its orbit – Saturn is one AU closer to the Earth and sun than when it’s at aphelion. At opposition in those years, Saturn lodges 8 AU from Earth and 9 AU from the sun. Saturn was last at perihelion on July 26, 2003, and will next reach perihelion on November 28, 2032.

The tilt of Saturn’s rings has a great impact on the planet’s overall brightness as seen from Earth. That’s why – although 2018’s opposition is distant, the planet isn’t particularly dim this year. In years when Saturn’s rings are edge-on as seen from Earth (2009 and 2025), Saturn does appear considerably dimmer than in years when Saturn’s rings a maximally titled toward Earth (2017 and 2032). Image via Wikimedia Commons.

Surprisingly, the year 2018 doesn’t present a particularly dim opposition of Saturn – although it’s a distant opposition. That’s because the tilt of Saturn’s rings plays a big part in Saturn’s overall brightness. In 2018, Saturn’s rings tilt almost the maximum 26^o toward Earth, reflecting sunlight our way. When Saturn’s rings are edge-on, as in the years 2009 and 2025, Saturn doesn’t reflect sunlight toward Earth so its brightness is reduced in Earth’s sky.

Bottom line: Let the moon be your guide to Saturn on May 30 and 31, 2018. This planet is now nearly at its best for 2018. Its opposition will come on June 27, 2018.

Tonight – May 31, 2018 – let the moon show you the ringed planet Saturn.

from EarthSky https://ift.tt/2L87flh